A new epoch

The changes made by us to the planet are so profound now that geologists are debating whether to recognise this period of human-induced planetary change as a whole new phase in the Earth's timeline: dubbed the 'Anthropocene'.

Next year the International Commission on Stratigraphy, a committee of the International Union of Geological Sciences, the group that compiles the Geological Timescale, will decide whether to adopt the Anthropocene as a new epoch in Earth's history.

This proposed new phase in the more than four-and-a-half billion year history of the Earth would mark for the first time a catastrophic phase of disruption of the planet's major systems as a result of the activity of a single species, us; Homo sapiens.

In the past, the Earth and life were rarely disrupted on a global scale, but when they were it was from by extraterrestrial impacts such as asteroids and meteorites or due to the cooling of the planet's layers early in its history.

These led to the loss of large numbers of species, shaping the course of the history of life and the planet itself.

Without these major extinction events we simply wouldn't be here as a species.

The beginning of the Anthropocene is generally regarded to be the year 1800, roughly coinciding with the start of the Industrial Revolution in Europe.

But, this seems like a rather arbitrary break point when we cast our eyes into the prehistoric past.

Too many mouths to feed

Well, we know that humans were responsible for changing the environment well before the Industrial Revolution began, many thousands of years before in fact.

One of the keys to understanding our growing impact on the environment is population growth.

Warren Hern of the University of Colorado estimated in the late 1990s the number of times the human population has doubled in its history.

He estimated that at 3 million years ago our population was doubling in size about every 500,000 years.

And by a million years ago the human population was doubling in size roughly every 100,000 years.

A big shift occurred around 25,000 years ago when our population began to double every 5,000 years or so; and the doubling time from then onwards started to shorten even more dramatically.

Between 10,000 years ago, roughly when farming began, and today, the human population has seemingly doubled almost 11 times leading to the presently more than 7 billion human inhabitants of the planet.

So, the human population has doubled as many times in the last 10,000 years as it did for the previous 390,000 years of our evolutionary history.

Demise of the megafauna

Now, this kind of modeling exercise might seem a little abstract, perhaps far removed from the realities of science or troubles of the planet.

Yet, some scientists think these massive increases in human population were the key reason why much of the world's megafauna went extinct between around 50,000 and 10,000 years ago.

This major extinction 'event' in Earth's history saw the loss of at least 200 mammal species weighing over 44 kilograms over a 40,000 year period.

This included our close evolutionary cousins the Neanderthals, Denisovans, and probably other bipeds as well.

As humans began to spread across the planet from our African birthplace around 70,000 years ago — probably because our population grew rapidly — we began to spill into Asia, Australia, Europe and eventually the Americas.

As we did so, our population grew even more; and we burned the landscape and introduced exotic species and diseases to most of the places where we settled.

We may even have taken advantage of the apparently unfearing megafauna, who probably didn't recognise us as predators, and hunted them to oblivion.

The slow reproduction rate of the megafauna mammals meant they couldn't adapt to human impacts and their populations probably collapsed; maybe not overnight; but certainly rather quickly on an evolutionary timescale.

Some scientists see parallels with the megafauna collapse and the Anthropocene.

A human population that has doubled in size more than 11 times since the end of the Ice Age; taking with it another 90 megafauna species that had managed to survive the great Ice Age megafauna collapse, but unable to survive the havoc we have wreaked since the invention of farming 10,000 years ago.

Stone pavements in the desert

The evidence for human alteration of the environment goes back much further though, with the crafting of the earliest stone tools, and may be even fire, at least 2.5 million years ago.

Earlier this month, Rob Foley and Marta Lahr from Cambridge University described in the journal PLoS One an archaeological site in remote Libya called Messak Settafet which shows pre-human populations were changing the environment for hundreds of thousands of years in the one place.

These early humans, belonging to species different to us — perhaps Homo erectus or Homo heidelbergensis - left stone tools and the waste of tool-making on the ground, building up over hundreds of thousands of years, perhaps beginning 900,000 years ago.

Remarkably, the ground at Messak Settafet is strewn in places with as many as 75 tools per square metre; it is, they suggest, a "pavement" of tools and manufacturing waste.

I've seen other sites in Africa myself where everywhere you turn you're literally walking over hundreds of tools left by our ancestors hundreds of thousands of years ago.

You get a sense at these places, in Africa mostly, that humans have been around for a very long time, and sometimes in abundance in the landscape: we've left our mark everywhere.

Connections in deep time

The more we learn about our deep time past the more we realise that humans and our ancestors have been altering the environment for as long as we've existed; as our ancestors did before us for hundreds of thousands, perhaps millions, of years.

The difference today is that there are more than 7 billion of us, and thanks to science, we're acutely aware of what we're doing; ignorance is no longer a defence.

Optimistically, with knowledge comes solutions and hope; we can learn from our past and take heart in the fact that change, in behavior, culture and technology, has served us well for millions of years.

Darren Curnoe will discuss this topic in more detail with Dom Knight on 702 Sydney tomorrow evening.

About the author:Associate Professor Darren Curnoe is an evolutionary biologist at the University of New South Wales. He writes about all aspects of evolution on his blog Walking on two feet. His work with colleague Ji Xueping is featured in the documentary Enigma Man: A Stone Age History. He also appears regularly on ABC 702.